These inventions apply to the only type of hot air ballon considered capable and feasible for the sustained manned flight and transport of one or more passengers. It was developed in the 1960's and is used principally for sport and recreation. The most popular size which will be described and used illustratively herein, is about fifty feet in diameter and provides a lift capacity of about 1500 pounds, far in excess of the volume of buoyant hot gas and lift required for normal use, i.e., short flights in the early morning or late afternoon.
Before 1960 the combustion required to heat and reduce the density of the balloon gas to render it buoyant was confined in an enclosure or furnace, an efficient system but limiting the rate of combustion to avoid destruction of the furnace and the balloon. It was not responsive to the need for rapid change in altitude for maneuverability and was too hazardous.
The present system employs one or more heavy duty propane burners each producing a large unconfined flame, operated intermittently by short blasts of combustion. Though inefficient and inherently handicapped it proved very practicable.
The buoyancy or amount of lift depends on the volume and average temperature of the gas contained in the balloon envelope which universally is made of synthetic fabric coated with a synthetic sealer having a maximum allowable operating temperature in the range 250.degree.-300.degree. F.
Because hot gas rises and accumulates under the ceiling of the balloon, temperature sensors are strategically located to indicate the temperature to the operator and enable him to manually control the temperature within safe limits, an operation requiring skill, experience and careful attention. The obvious potential hazards of this present system are eliminated by the invention, as explained hereinafter.
It is briefly noted here, and fully explained below, that one component of the invention comprises a diaphragm of envelope or similar material suspended horizontally and slackly beneath the balloon ceiling and above the equator, by tension members connecting a multiplicity of points on its periphery to points on the envelope. Sufficient distance is provided, between the diaphragm and the envelope to allow the passage of gas. This component constitutes a subceiling having three simultaneous automatic functions: 1, to intercept radiant energy from the flame, convert it to heat and transfer it to the contiguous gas; and, 2, to intercept the radiant energy from the sun that enters the balloon through translucent portions of the ceiling, convert it to heat and transfer it to the contiguous gas: 3, to provide a subceiling to accumulate a pocket of hot gas to augment buoyancy or lift. These three functions have the common purpose and ability to increase the average temperature of the gas to provide the buoyancy or lifting capacity of the balloon. The specification deals with these functions in order.
These inventions improve "hot air" balloons and the heating of the gases within them, the heat being supplied by one or more flames of burning propane. In one popular model, the incandescent portion of the products of combustion, the flame, is in the form of a vertical column about twelve-fifteen inches in diameter extending about six feet high, measured from the burner orifice or orifices; this size of flame is typical of modern hot air balloons.
MARKS Mech. Eng. Handbook, 8th Ed. 4-78 states: "Radiation from carbon dioxide and water vapor (combustion products) occurs in spectral bands in the infrared. In magnitude it overshadows convection at furnace temperatures." It is also known that the amount of radiant energy emitted by a substance increases as the fourth power of the temperature. Therefore it is evident that the amount of radiant energy emitted by burning propane having a flame temperature of 3500 deg. F. is greater than the convected heat energy.
The rate of combustion of a balloon burner is enormous. What makes its use possible is the system of very short combustion periods which not only reduces the rate and amount of energy transmitted but enables self-cooling of the heated object between combustion periods.
Gases are practically transparent to radiant energy and therefore are not heated by it. Radiant energy travels in straight lines in all directions from every point on the flame and rising column of hot combustion products until it is intercepted by some opaque object within the balloon or until it is intercepted by the balloon envelope when it is converted to heat energy. Some of the heat is transferred to the interior gas by conduction and convection, and some is lost to the outside atmosphere. I have discovered that at least one modern balloon envelope material is translucent radiant energy, a substantial amount from the flame passing outward and that from the sun, solar energy, passing inward. These inventions include the utilization of the radiation from both sources.
With respect to the radiant energy converted to heat energy by and within the envelope material, the amount lost to the outside and the amount transferred to the gases within the balloon are indeterminate, but it is evident that the former greatly exceeds the latter because the temperature gradiant (under normal conditions at altitude) is much steeper downward to the outside atmosphere than to the inside. From the above considerations I have concluded that the former method of heating the gases within the hot air balloon is inherently handicapped by the fact that most of the energy released by the combustion process passes through the gases without heating them and, when finally converted to heat energy by and within the envelope material, most of the heat is lost to the outside atmosphere. My inventions utilize practically all of the energy formerly lost.
Recapitulation: former losses of energy from within the balloon through the envelope to the outside atmosphere have been: 1,--some of the radiant energy from the flame passed through the envelope, if it was translucent; 2,--most of the radiant energy converted to heat by and within the envelope material was lost to the outside atmosphere; and, 3,--heat from the hot interior gas, conveyed to the inside surface of the envelope, passed through it by conduction, and then heated the boundary layer of the outside atmosphere by conduction and was conveyed away and lost. My invention prevents the loses described in 1 and 2. Under certain conditions, as will be seen, the loss as in 3 can be reversed by my invention, by augmenting the amount of solar radiation entering the balloon and converting it to heat.